38 THE STRUCTURE AND LIFE OF BIRDS cuHap, 
white and have blue eyes, are generally deaf. Pigeons. 
with short beaks have small feet, and those with long 
beaks large feet. In wild animals the right and left 
sides always vary very nearly in the same way. The 
front and hind limbs often vary together, and even the 
jaws and limbs. He maintains that parts which are 
homologous—for instance, arms and legs—often show 
similar tendencies. Length of arm in men generally 
goes with height, and if a child has long hands, people 
infer that it will be tall. Possibly, then, through corre- 
lation the lengthening and strengthening of the fore limb 
might be accompanied by a lengthening and strengthen- 
ing of the hind limb. Ofcourse, it cannot be looked upon 
as an invariable law that variation follows the lines of 
homology. The fore legs of a giraffe have altogether 
dwarfed the hind legs. The tendency of such varia- 
tion has been to lift the giraffe’s head higher, so that 
in times of drought, when other cattle were dying of 
Kunger, he might browse on the higher branches of 
the trees. A corresponding growth of the hind legs 
would have been waste of material, and possibly this 
may have caused the weeding out of those whose hind 
legs developed parz passu with their fore legs. 
The difficulty of tracing back the course of develop- 
ment is undeniably great in the case of any animal, and 
he who attempts it is apt to lay himself open to ridi- 
cule. The cautious exponent of evolution takes refuge 
in generalities. It is more ingenuous, andin every way 
better, to face the difficulties, while at the same time 
confessing that much more evidence is wanted from 
fossil remains before we can fill in the blanks. At 
present the position of the evolutionist is somewhat, 
